This invention relates to a cup member for use in a color cathode ray tube in controlling three electron beams emitted from an in-line electron gun.
A color cathode ray tube is already known, which comprises an in-line electron gun. Three electron beams emitted from the in-line electron gun as a central beam and outside beams, are deflected horizontally and vertically by a deflection yoke disposed in a funnel portion of the cathode ray tube to form rasters on a phosphor screen through a shadow mask. A coma aberration generally arises due to a deflection sensitivity difference between the center and the outside beams. The coma aberration has been minimized by adjusting a horizontal deflecting magnetic field produced by the horizontal deflection yoke in a known manner. Despite the adjustment, it has been impossible to perfectly clear off the coma aberration. As will later be described more in detail, a cup member is used for the three electron beams with a view to perfectly clear off the coma aberration.
A conventional cup member has, however, insufficient to perfectly clear off the coma aberration when a high horizontal deflecting frequency is used to the cathode ray tube.